Data transmitting and indicating system



June 22, 1948.

Filed July 22, 1942 W. KOENIG, JR

DATA TRANSIITTIXG AND INDICATIHG SYSTEM 4 Sheetsi-Sheet 1 FIG. 2

INVENTUR m KOEN/G, JR.

AT TORNEV June 22, 1948.

W. KOENIG, JR

DATA TRANSMITTING AND INDICATING SYSTEM Filed July 22, 1942 4 Sheets-Sheet 2 35 FIG 3 "I" 3o u Ann AM Aug 57 WVVV I'I'I' "I!" l 0 0 2a -w as INVENTOR ATTOPNFY June 22, 1948. w. KOENIG, JR

DATA TRANSMITTING AND INDICATING SYSTEM 4 Sheets-Sheet 3 Filed July 22, 1942 INVENTOR W KOENIG, JR. fl /M ATTORNEY June: 22, 1948. w. KOENIG, JR 2,443,623

I DATA TRANSMITTI ENG AND INDICATING SYSTEM Filed July 22, 1942 4 Sheets-Shet 4 [WE N 70/? n. mew/a, JR.

Patented June, 22, 1948 DATA TRANSMITTING AND INDICATING SYSTEM Walter Koenig, Jr., Clifton, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 22, 1942, Serial No. 451,857

registering instrumentality at a transmitting station.

Another object of the invention is to provide manually operable means for controlling the substantially synchronous reproduction of a reading at a receiving station in order to compensate for changes in the rate of variation of the reading at the transmitting station.

Another object of the invention is to provide an improved speed regulator device for an electric motor.

Another object of the invention is to provide for arresting continuously driven registers for the purpose of taking a reading while the driving mechanism therefor continues to operate and ac cumulate movement, and to bring the registers into step with the driving mechanismupon release of the registers.

Another object of the invention is to automatically reverse the connection and alter the sensitivity of a polarized current responsive device upon sudden reversal of the direction and increase in the amount of current applied thereto.

In general the invention contemplates the association with a registering instrumentality at a transmitting station of potential dividers for units and fractions of units of measurement of a quantity or characteristic. The potential dividers are so associated with the registering instrumentality that the potential divider which represents fractions of units is operable through one full cycle, or revolution in the case of a circul-ar potent al divider, for each unit of measurement and the potential divider which represents units encompasses a convenient plurality of such units in one cycle or revolution of operation.

The potential dividers at the transmitting station are connected across two power supply conductors which extend to the receiving station where potential dividers of an equal number and kind are connected across the two conductors. A source of direct current signaling potential at the receiving station is connected across the two power supply conductors through potentiometers 8 Claims. (Cl. 177-351) by means of which compensation may be made for variations in the resistance of the two power supply conductors. The contactors of the potential dividers at the transmitting station are connected through individual conductors to the contactors of the corresponding potential dividers at the receiving station and each of these conductors has associated with it at the receiving station and preferably also at the transmitting station, a current registering device such as a galvanometer.

The contactors of the potential dividers at the receiving station are interconnected through gearings so as to be operable in the same ratio as the contactors of the potential dividers at the transmitting station. Preferably there is associated with each of the potential dividers at the receiving station a scale and pointer indicating device whereby the settings of the potential dividers may be observed visually in terms of units and fractions of units of measurement at any time. Although a manually operable driving means for the contactor at the receiving station is provided, it is preferable to provide also a power-driven mechanism for driving the contactors of the potential dividers, with manually operable means for varying the speed of the driving means and with regulator means for maintaining the speed of the driving means constant for any setting of the manually operable speed controlling means.

With the power supply lines properly balancedv with respect to their resistance, any discrepancy between the settings of the potential dividers at the transmitting station with reference to the potential dividers at the receiving station will result in a potential difference between the ends of the conductors which control the galvanometers, so that current will flow through those conductors and the galvanometer armatures and pointers will be deflected from their zero positions. This discrepancy may be eliminated and the contactors of the potential dividers at the receiving station brought into exact correspondence with the contactors of the potential dividers of the transmitting station by rotating the contactors at the receiving station in the direction to reduce the deflection of the galvanometers until the galvanometers show zero deflection.

When the measurement being registered by the registering instrumentality at the transmitting station is continuously varying in the same direction at substantially uniform rate, the power driving mechanism for the contactors at the receiving station may be operated at such speed under the proper adiustment of the manually dividers at the receiving station at all timesindicate the reading of the registering inst tality at the transmitting station. It

ens also within the contemplation of the invention to provide similar power-driven mechanism with mantial divider at the receiving station for opening I and closing. therenergizing circuit of the relay end contacts, that contactor and the correspond-' ing contactor atthe transmitting station are disually operable speed variation control for driving the registering device and the associated potential divider contactors atthe trasmitting station, to cause the registering instrumentality to register continuously the value of the characteristic that is being measured where such value is changing at substantially uniform rate.

In case the potential divider contactors at the receiving station are permitted to lag behind the contactors at the transmitting station to the extent that a potential divider contactor at the transmitting station moves across the gap from one of the end contacts to the other, before the contactor of the corresponding potential divider at the receiving station leaves the corresponding end of its potential divider, the full potential of the power supply will be applied between the ends of the galvanometer conductor associated with the contactors. This causes extreme deflection of the galvanometer in the reverse of the direction in which the potential divider at the transmitting station had been previously tending to deflect it and gives an apparent, indicationthat the contactor at the receiving station should be reversed to restore zero reading of the galvanometer. To prevent the occurrence of this'false indication and also the extreme deflection of; the galvanometer, the receiving station is provided with a rectifier associated with each of the galvanometer conductors and each of the rectifierscontrols a relay which is effective to reverse the connection of the g-alvanometer to its conductor and also to reduce. the sensitivityof the galvanometer when the full potential between the power supply conductors is impressed across the ends of a galvanometer conductor.

In accordance with an alternative embodimerit of the invention, corresponding potential dividers at the transmitting station and. receiving station are provided with two diametrically opposed contactors insulated from each other and driven as a single element. The contactors I at the transmitting station are connected through individual conductors to front and back contacts of a relay, the cooperating armature of which is connected through a galvanometer to another armature of the relay, the cooperating front and 'back contacts of which are connected to the two contactors of the potential divider at the receiving station in the same relation as the contactors of the potential divider at the transmitting station. When .the relay is energized one of the contactors at the transmitting station is connected through the front contacts and armatures of the relay and through the galvanometer to the corresponding contactor of the potential divider at the receiving station. When the relay is deenergi zed the other contactor at the transmittingstation is connected through the back contacts and armatures of the relay and through the galvanometer to the corresponding contactor of the potential divider at the receiving station. Switching contacts are associated with the pot n- 'vices at the receiving station and speed regulated in such relation to the movementof the contactors the. "when either contactor is within a predetermined distance of the end contact of the potential divider, and therefore is in prospect of passing directly from one to the other of the connected from the galvanometer, by the relay, and the other contactors are connected to the galvanometer. This arrangement prevents the sudden connection to the galvanometer of the full voltage across the potential divider due to passage of a potential divider contactor directly from one of the end contacts'to the other.

For a complete understanding ofthe invention, reference may be had to the following detailed description to be interpreted in the light of the accompanying drawings wherein:

Fig. 1 is a schematic perspective view showing the data registering device at the transmitting station with the potential dividers associated therewith; v

Fig. 2 is a circuit diagram of the electrical system at the transmitting station;

Fig. 3 is a circuit diagram showing the electrical system at the receiving station;

Fig. 4 is a schematic perspective view showing the potential dividers and data registering dely to Fig. 1, the reference numeral ll designates an optical device through which a distant object may be observed. Optical device H is supported by horizontally extending trunnions in a U- shaped bracket I2 which is secured to a vertically extending shaft 1'3. Shaft I3 is keyed or otherwise secured to a worm wheel 14 which is engaged by a worm l6 secured to a shaft IT. The ratio between worm wheel .14 and worm I6 is preferably 360 to 1 so that optical device II is moved through an angle of 1 degree in a horizontal plane for each revolution of shaft ll.

Shaft I! has secured thereto a crank wheel It by means of which rotation may be imparted to the shaft and also has secured thereto a contact arm IQ of a potential divider 21 which is stationarily mounted. Potential divider 2i preferably has 100 uniformly spaced electrical contacts arranged in a circle so that movement of contact arm I!) from one contact to the next will represent /1oo of 1 degree of movement of optical device II. V v

A pinion 22 secured to a shaft 23 meshes with the worm wheel l4. Shaft 23 has secured thereto the contact arm 24 of a potential divider 26.

Due to considerations of physical dimensions, it is considered preferable not to attempt to provide 360 contacts on the potentiometer 26, one to represent each angle of are through which optical device H may be rotated, and preferably a smaller number of B contacts is provided which number is a factor of 360 such as 30, for example. With that number of contacts contained in potentiometer 26, the ratio of the number of teeth on the worm wheel 14 to the n umberof teeth on pinion 22 would be 12 to 1 50 that p0- te i meter' c ntact arm 24 would execute exactly I 5. twelve revolutions for one revolution of optical device H, and advancement of the contact arm from one contact to an adjacent contact represents 1 degree of angle of rotation of the optical tial divider 28, which rotates steadily as' the worm wheel I4 is rotated steadily, shall not correspondingly advance steadily from one contact to another, but shall remain in engagement with 'ment between cam I0 and pin I5. Allnk 25 connects bell crank 29 to the housing of potential divider 25 and this housing is mounted for limited angular rotation about its axis. The rate of change of the radius of cam I0 is such that it imparts to the housing of potential divider 26 angular movement which is equal to that imparted to contact arm 24 by worm wheel [4 through pinion 22, so that throughout a very large portion of each revolution of cam ill-there is no relative movement between contact arm 24 and the potential divider housin 26 and thus there is no relative movement between the contact arm and the contact which it is engaging. As the sharp drop off in cam I0 traverses follower pin it: going in either direction, the housing of potential divider 26 is quickly shifted with respect to the contact arm 24 to bring one or the other of the adjacent contacts into engagement with the contact arm 24. Cam In is so oriented with respect to potential divider contact arm l3 that the shifting of the housing of potential divider 26 with respect to contact arm 24 begins and ends at substantially equal angular distances each side of the zero position of potential divider contact arm it), such as from .99 degree to .01 degree.

The two potential dividers appearing in Fig. 1

are shown in schematic form in Fig. 2, identified by the same reference numerals. Although the potential dividers have been shown in Fig. 2 as comprising continuous resistance windings and slider contact arms, a simple wa in which such potential dividers may be constructed from a practical standpoint is to provide fixed resistors of equal value bridgin each two adjacent contacts, with the exception that one such pair of contacts has no bridgin resistor and the source of potential difi'erence which is to be distributed over the potential divider is connected to these two contacts.

The hundredths of a degree and degree Potenterminal of the middle bank of a three-point three-bank switch 33 and also to one terminal of each of the potential dividers 36 and 31 which are hundredths of a degree and whole degree potential dividers respectively and are identical with the potential dividers 2| and 26, respectiveis. at the transmitting station. The other terminal of potentiometer 32 is connected through resistor 33 to the lower contact of the middle bank of multiple bank switch 33 and to the other or left-hand terminals of the potential dividers 3i and 31. The contactor of line balancing potentiometer 3| is connected to battery of one polarity and the contactor of line balancing potentiometer 32 is connected to battery of the opposite polarity. These two contactors may be connected to the terminals of one battery or other source of direct current potential.

The contact arm i9 of hundredths degree potential divider 2| is connected to one terminal of a galvanometer 33, the other terminal of which is connected to galvanometer line conductor 33 which extends to the receiving station and is connected to one end of a series of resistors 4|, 42 and 43. The other end of this series is connected to the switch arm of the upper bank of switch 33 and from the middle contact of the upper bank, which is the contact engaged by the switch arm except when line balancing operations are in progress, as will be described later, is connected through conductor 44 and normally closed key 46 to the contact arm of hundredths potential divider 36 at the receiving statial dividers 2| and 26 are each bridged across tion. Similarly, the contact arm of the whole nal of which is connected to a second galvanometer line conductor 48 which extends to the receiving station and connects to the right-hand end of a series of resistors comprising the resistors 5!, 52 and 53, the left-hand end of which is connected to the lower switch arm of switch 33. The middle contact of the lower bank of the gang switch is connected'by conductor 54 to the con! tact arm 50 of the whole degree potential divider 31 at the receivin station.

The input terminals of a full wave rectifier are connected to the terminals of resistor 43 so that the rectifier is in shunt with the resistor and the winding of a spring-biased polar relay 51 is connected across the output terminals of the rectifier 58, The back contact of relay 57 is connected to the right-hand terminal of resistor 4| and the armature of the relay is connected to one terminal of a galvanometer 58, the other terminal of which is connected to the left-hand end of resistor 4|, Thus when relay 51 is deenerglzed, current flowing through resistor 4| in either direction 'will develop a potential difference across this resistor and this potential difference will be impressed across galvanometer 58 to produce a corresponding deflection of the galvanometer. The front contact of relay 51 is con nected through a resistor 59 to the left-hand terminal of resistor 42 and the latter resistor has the same value as resistor 4|. Thus when relay 51 is energized, galvanometer 58 will be connected across resistor 42 instead or across resistor 4| and in the reverse direction or polar sense, and in addition resistor 59 will be connected in series with galvanometer 58 to limit the flow of current through the galvanometer resulting from the potential difierence across resistor 42.

Similarly, the input terminals of a full wave rectifier 6| are connected across resistor 53 and a polar relay 62 is connected to the output termlnalsgoi rectifier 3|. A resistor 83 is connected between the left-hand end of resistor 32 and the -front contact of relay 32 and the back contact of the relay is connected to the right-hand end of resistor The armature of relay 32 is connected to one terminal of a galvanometer 34, the other terminal of which is connected to the lefthand end of resistor 5 Since the communication system shown .in the combination of Figs. 2 and 3 serves only to communicate the setting or movement of the optical device shown in Fig. 1, a supplemental two-way communication system for transmitting other intelligence between the transmitting and receiving stations is assumed.- Such supplemental communication system may be telephone or telegraph. In order to balance the resistance of the power supply lines 21 and 28, whiclioperation is performed at the receiving station, the attendant at the receiving station communicates to the attendant at the transmitting station instructions to adjust the hundredths degree potential divider so that the contact arm engages the.

contact to which power supply line conductor 21 is directly connected. It has been'found convenient to so relate the hundredths degree potential from which it will follow that the zero contact willbe about at the midpoint of the potential divider, Accordingly, the attendant at the receiv-- -ing station may instruct the attendant at the sending station to adjust the crank wheel l8, which may be graduated to the scale of 10.0, to the setting 50. The attendant at the receiving station, thereupon operates switch 33 to bring the switch arms into engagement with the upper contacts of the three banks.

The operations outlined in the foregoingparagraph establish a Wheatstone bridge circuit having the batteries 66 and 31, which have their positive and negative poles respectively connected to the contact arms" of the potentiometers 3| and 32, respectively, connected in series-aiding relation across two oppositeapices of .the bridgecircuit and the galvanometer conductor 39 and resistors 3|, 2 and 43 in series therewith connected across the other two apices of the bridge circuit. One of the arms on the positive battery side of the bridge includes the power supply conductor 21 and the portion of potentiometer 3| between that power supply conductor and the contact arm of potentiometer 3|. The other arm on the same side of thebridge includes only the remaining portion of potentiometer 3| andresistor 33. The arm on the negative battery side of the potentiometer adjacent to that which contains power supply conductor 21 includes the. pair. of potential dividers 2| and 26 which are is open at the upper contact arm of switch 33 so that there will be no division of current in the potential divider 33.

With the apparatus thus arranged the contact 8 arm of potentiometer 3| is adjusted until the galvanometer indicates zero current in the galvanometer conductor 33, which is an indie cation that the Wheatstone bridge circuit has been balanced. Thereupon the operator at ,the receiving station instructs the attendant at'the transmitting station to move the crank wheel l3 to the setting 5|, which is at the left-hand endof the winding of the potential divider. The operator at the receiving station moves the switch arms of switch 33 into engagement with the l6wer contacts. The effect of these two' operations, the meat the transmitting station involving changing. the position of potential divider contact arm I9 and the one at the receiving station involving switching of switch 33 is to transfer the set of potential dividers 2| and 28 and the set of potential dividers 36 and 31 out of the arms of the Wheatstone bridge circuits which receive negative battery and into the adjacent arms which receive positive battery,-so that the two pairs of potentialdividers have been moved from one side of the galvanometer circuit to the other side. Potentiometer 32 is then adjusted until the galvanometer '58 gives a zero reading. 7

Upon switching back to the first condition, namely, with potential divider contact arm l3 engaging the contact representing a reading of /100 and switching the gang switch contact arms back to their upper contacts thefirst established balance may be found to have been disturbed, particularly if the adjustment of potentiometer 32 was substantial. The bridge circuit may be rebalanced by readjusting potentiometer 3|, By this method of alternately rebalancing of the bridge circuit for the two different sets of connections, by means of potentiometers 3| and 32, a condition may be achieved in which no unbalance will appear upon switching from one to the other of the two bridge circuit conditions. Since the resistance of potential divider 2| is the same as that of potential divider 36 and the resistance of potential divider 26 is the same as that of poteritial divider 31, the over-all resistance of each 'parallelly connected pair of potential dividers is the same, and since transference of the two pairs of potential dividers from two arms of the bridge on one side of the galvanometer, to

the two rams on the other side does not disturb the balance of the bridge, it follows that the-two arms on one side of the galvanometer conductor contain equal total resistance with or without the potential dividers and. the two arms on the other side of the galvanometer conductor contain equal total resistance with or without the potential dividers. Were this not true, the insertion or removal of the pairs of potential dividers wouldcalter the ratios between arms on either side of the galvanometer conductor and wouldunbalance the bri e A or in ly, it follows that with the bridge circuit thus balanced the resistance of powor supply conductor 21 plus the resistance of that portion of" potentiometer 3i between conductor 21 and the contact arm of potentiometer 3| is equal to the resistance of the remainder of that potentiometer plus the resistor 30. Similarly, the resistance of power supply conductor 28 plus the resistance of that portion of potentiometer 32 between conductor 28 and the contact arm of potentiometer 32 is equal to the resistance of the remainder of that potentiometer plus resistor 35. The resistance of the power supply conductors 2! and 28 has thus been balanced at the receiving station and this balance may be checked from time to time and balance restored if it is found that the resistance of power supply conductors 21 and 28 has changed materially. Upon completion of a balancing operation the switch arms of switch 33 are restored to the middle contacts of the three banks of contacts and the system is thus placed in condition for reproducing at the receiving'station continuously varying readings of the optical device H at the transmitting station. When the optical device II is trained on a distant moving object the movement of which is to be followed, the-attendant at the transmitting station informs the operator at the receiving station over the supplemental telephone or telegraph system, hereinbefore mentioned, of the degree reading of the optical device since the potential divider 26 and its companion potential divider 31 represent only a fraction of a full revolution of optical device H, such as 30 degrees, as previously set forth by way of example. One revolution of potential divider contact arm 24, therefore, represents a sector corresponding to 1 s of'a revolution of shaft l3 and the attendant at the transmitting station need inform the operator at the receiving station only as to the identity of the sector in which optical device II is disposed.

Assuming that at the time that the attendant at the transmitting station trains optical device I l upon a moving object and begins to follow the movement of that object by rotating crank wheel t8, the contact arms of potential dividers 36 and 31 occupy. random positions not corresponding to the contact arms of potential dividers 2| and 26. potential difierences will be impressed upon the galvanometer conductors 39 and 48 which will cause galvanometers 38 and 41 and galvanometers 58 and 64 to be deflected from their zero positions. It is then incumbent upon the opera- ,.tor at the receiving station to rotate the contact arms of potential dividers 36 and 31, by means which will be described in detail hereinafter, to reduce the deflection of galvanometers 58 and. to zero. The operator can tell by the direction of deflection of the galvanometers in which direction the contact arms should be moved to reduce the deflection to zero, and the controllin means may be arranged so that operation thereof in the same direction as the galvanometer defiection will increase the deflection and operation in the opposite direction will reduce the deflection. As the contact arms of potential dividers 36 and 31 are brought into positions corresponding to those of the contact arms of potential dividers 2| and 26, the current in the galvanometer conductors 39 and 48 will be gradually reduced until the galvanometers read zero. The attendant at the transmitting station is presumably rotating crank wheel |8 continuously to keep the optical device trained on the moving object and therefore is continuously unbalancing the system. However, the operator at the receiving station continuously moves the contact arms of potential dividers 36 and 31 in an attempt to maintaingalvanometers 58 and 64 at zero readingsand to the extent that the operator succeeds the contact arms of potential dividers 36 and 31 will be kept in substantial synchronism with the contact arms of potential dividers 2| and 26. The attendant at the transmitting station is informed at all times as to the actions of the operator at the receiving station with reference to potential dividers 36 and 3! because the galvanometers 38 and 41 are contained in the galvanometer conductors 38 and 48 at the transmitting station and will indicate failure of the operator at the receiving station contnuously to rebalance the system as the attendant atthe transmitting station continuously unbalances it.

As long as the potential dividers at the receiving station are kept substantially in synchronism with those at the transmitting station there will be verylittle current flowing in galvanometer conductor 39 and an insufficient potential difference will be developed across resistance 43 to operate relay 51, so that the relay will remain dcenergized. If the potential dividers at the receiving station lag slightly behind those at the transmitting station the current through resistors 4|, 42 and 43 will be in one direction and galvanometer 58 will be deflected to one side whereas if the potential dividers at the receiving station lead those at the transmitting station slightly the current through the resistors 4|, 42 and 43 will be in the opposite direction and the galvanometer 58 will be deflected in the opposite direction. Since the movement of contact arm 24 with reference to potential divider 26 is step by step and that of potential divider 31 is also step by step, as in the case of potential dividers 2| and 26, there is little likelihood of unbalance being indicated by galvanometer 64 after the two sets of potential dividers have been brought substantially into synchronism, except when either of the potential dividers 2| or 36 moves through the zero position and the other has not yet moved through the zero position due to a slight lag between them.

When the contact arm of potential divider 2| moves from the contact representing to that representing /100 it leaves one end of the potential divider and moves into engagement with the oppositeend. In so doing it goes directly from one battery polarity to the other. Assuming that the contact arm of potential divider 36 is lagging slightly and has not yet left the position corresponding to a reading of /100 of a degree, the entire supply voltage will be impressed on the galvanometer conductor 39 and the current will be in the reverse direction to that previously existing because of the change in polarity at the contact arm of potentiometer 2|, and a relatr'ely large current will flow through resistors 42 and 43 in the opposite direction to the small current previously flowing. The large potential difference thus developed across resistor 43 will operate polar relay 51 through rectifier 56 and the current through the relay will be in the same direction regardless of which end of resistor 43 is positive, Relay 51 becoming energized connects resistor 59 in series with galvanometer 58, and connects this series circuit across resistor 42in the reverse direction relative to the previous connection of galvanometer 58 across resistor 4|. With the current through resistor 42 now reversed and the connection of galvanometer 58 also reversed, the operator at the receiving station will continue to move the contact arm of potential divider 35 in the same direction that he had previously been moving it and in the specific example outlined herein, will move the contact arm across from the righthandend of potential divider 36 to the left-hand end. Were it not for this reversal of the connection of galvanometer 58 the galvanometer would be deflected in the opposite direction upon the reversal of current through resistors 4|, 42 and 43 which reversal the operator might interpret as necessitating reverse rotation of the contact arm of potential divider 88 in order to restore balance. Such reverse movement would restore balance eventually from the standpoint of galvanometer conductor 89 but would unbalance the system from the standpoint of galvanometer conductor 48 because the backward movement of the contact arm 45' of potential divider 38 relative to that of potential divider 2| would also result in backward movement of the contact arm 58 of potential divider 81 relative to that of potential divider 26. With the reversing arrangement comprising rectifier 88 and relay 5! the operator receives no false indication when the potential divider contact arms move across the gap in the potential dividers. The series resistor 89 reduces the current through galvanometer 58 so that the galvanometer is not deflected ofi scale.

Galvanometer 60 has associated vwith it the same type 'of protective arrangement comprising the rectifier SI and the polar relay 82 for preventing a false indication when the contact arm of one of the full degree registering potentiometers 28 and 31 moves across the gap of its potential divider ahead of the contact arm of the other. It is to be noted that the galvanometers 38 and Al are not shown as being provided with a reversing and current reducing system consisting of a rectifier and relay operated thereby. They could be provided with such supplementaD-apparatus if desired but since in the normal mode of operation observations being made at the transmitting station are transmitted to the receiving station, so that the burden is upon the operator at the receiving station to follow the potential dividers at the transmitting station, the fact that the galvanometers 88 and ll may on occasion deflect suddenly in the reverse direction and through a wide arc, is of no consequence because the attendant at the transmitting station is not ordinarily dependent upon indications of the galvanometers 88 and 81 for instructions as to the operation of potentiometerg 2i and 20.

Occasions may arise, however, for operation of the system in the reverse direction. For example, it may be desired to instruct the attendant at the transmitting station to scan another area for an object or to train the optical device on another object, the general location of which with reference to the transmitting station, the operator at the receiving station is informed. Accordingly, the receiving station may instruct the transmitting station by telephone or telegraph as to the sector in which the scanning of an area for another object or in which the training of optical device II upon another object is to be done and the operator at the receiving station may then adjust the contact arms of the potential dividers 38 and 37 to positions representing the degree and hundredths of degree position at which scanning of an area for an object by means of optical device II is to be performed. Under these circumstances the operator at the receiving station will unbalance the system in so adjusting 12 Whereas Fig. 1 shows how the contact arms of potential dividers 2| and 26 may be operated manually, Fig. 4 shows a system for driving the contact arms of potential dividers 36 and 81 by means of a variable speed motor, with means for varying the speed of the motor so that when the optical device II is being rotated at a substantially uniform rate in following a moving object,

the contact arms and of the receiving potential dividers 88 and 8i may be driven at the same uniform rate to continuously rebalance the po- ,,tential divider system as it is continuously unbalanced at the transmitting station.

In Fig. 4 the contact arm 85 for the hundredths degree potential divider 86 is fixed to a shaft 18 which has secured thereto a worm wheel 11. Worm wheel II meshes with a worm gear I8 secured to a shaft I8 which has secured thereto a cross arm 8| which supports at the opposite ends thereof freely rotatable beveled planetary gears 82 and 83. Shaft 19 supports a sleeve 84 which has at one end a beveled gear 80 meshing with the planetary gears 82 and 88 and at the other end a worm wheel 81, the beveled gear 88 and worm wheel 81 being fixedly 'secured to sleeve 88.

Shaft I9 also supports a sleeve 88 which has secured to one end a. beveled gear 88 meshing-with the planetary gears 82 and 83 and which has secured to the other end a beveled gear 9i. A beveled gear 92 in mesh with the gear 9| is secured to a shaft 93 which also has secured thereto a worm wheel 94 which meshes with a worm gear 96 secured to ashaft 9'I.- Shaft 01 also has I secured thereto a crank wheel 98.

A full degree potential divider 31 has its contact arm 50 fixed to a shaft IN. The shaft IOI has secured thereto a worm wheel I02 which meshes with a worm gear I03 secured to a stub shaft I05. Shaft I08 has secured thereto a worm wheel I08 which meshes with a worm gear I01 secured to a shaft I08. Shaft I08 has secured thereto a cross arm I08 which rotatably supports beveled planetary gears II I and H2, which structure is comparable with the cross arm- 8| and the planetary gears 82 and 83. Shaft vIIIBsupports a sleeve H3 which has secured thereto atone end a beveled gear I I4 and at the other end a beveled gear H8. Beveled gear IIII meshes with a companion beveled gear Ill secured to a shaft H8 which also has secured thereto a crank wheel I I8. Beveled gear I I8 meshes with the planetary gears III and H2. Shaft I08 also supports a sleeve IZI which has secured to the ends thereof beveled gears I22 and I28. Beveled gear I22 meshes with the planetary gears II I and I I2 and beveled gear to sleeve 86. There is a considerable gear reducimpart rotation to shaft 93 but that shaft 93 cannot impart rotation to shaft 31 through the gears 34 and 88. Thus with shaft 83 held stationary due to the non-reversible characteristic of the drive, sleeve 88 and beveled gear 88 are held stationary through beveled gears SI and 32. Beveled gear 88 in rotating causes planetary gears 8| and 82 to roll in engagement with stationary beveled gear 89 in accordance with the well known planetary or differential gear action and the planetary gears, in rolling against stationary gear 83 impart rotation to shaft 19 through cross arm 8|. shaft 13 will be one-half the speed of sleeve 84 as is also well known in power transmitting mechanisms of this type so that a further speed reduction takes place in the planetary gear mechanism and a still further speed reduction occurs in the gearing comprising worm gear 18 and worm wheel 11 between shaft 19 and the hundreds potentiometer contact arm shaft 18.

Shaft 19 imparts rotation through beveled gears I23 and I24, through the planetary gear mechanism comprising beveled gears I22 and H8 and The speed of rotation of planetary gears III and H2, through shaft I08,

gears I81 and I88, shaft I84, gears I03 and I32, and shaft IIII to the contact arm 50 of potential divider 31. Beveled gear I I1 is provided with two diametrically opposed rccwes I3I, and a spring detent I32 engages one or the other of the recesses I3I and holds gear II4, sleeve H3 and gear IIIi stationary so that planetary gears IIIv and H2 roll against gear H8 in imparting rotation to shaft I08.

The speed reduction provided at the several points previously described between shaft 19 and shaft IIII is such that the contact arm 58 of potential divider 31 moves through the distance from one potential divider contact to another while the contact arm of potential divider 38 rotates through a full revolution, which is comparable with the relative speeds of rotation of potential divider contact arms I9 and 24 in Fig. 1. It will be understood that the shaft 18 will be provided with the same time of cam and follower mechanism as that shown in Fig. 1 for causing the housing of potential divider 31 to move uniformly with its contact arm except when the contact arm associated with potential divider 36 is passing through its zero position in either direction, whereupon the housing of potential divider 31 will be shifted one way or the other with respect to its contact arm as is fully described in connection with Fig. 1. The cam and follower mechanism for shifting the housing of potential divider 31 has been omitted from Fig. 4 for the sake of simplicity.

If it is desired to operate the contact arms of potentiometers 38 and 31 manually instead of by the aided tracking mechanism comprising motor driven shaft I21, this may be accomplished by means of manually operable crank 88. The drive will be imparted through bevel gears 92 and 3|, sleeve 88, bevel gear 89 and planetary gears 82 and 83 to shaft 19. The gearing comprising worm gear I26 and worm wheel 81 is a non-reversible drive similar to worm gear 38 and worm wheel 94, in the sense that shaft I21 cannot be rotated from sleeve 84, so that gear 88 will be stationary and planetary gears 8I and 82 will roll against it. Operation of shaft 19 by manual operation of crank 98 will probably be feasible only under the circumstance that very slow rotation of shaft 18 is required to keep the potential divider system balanced because there is a gear reduction between shafts 81 and 83, a 2 to 1 reduction between sleeve 14 83 and shaft 13 through the lanetary gear mechanism and a further reduction between shaft 18 and shaft 18 through worm gear 18 and worm wheel 11 so that it may not be possible to rotate shaft 31 sufliciently fast manually to cause shaft 18 to track with shaft I1 of Fig. 1 and keep the potential divider system balanced. Manual operation of shaft I1 in Fig. 1 is entirely feasible because crank I8 is directly secured to shaft I1, although it will be understood that power driven aided tracking mechanism similar to that shown in Fig. 4 may be employed if desired at the transmitting station shown in Fi 1.

The speed of motor I28 is controlled by a magnetic drag unit associated with the rotor shaft I21 of motor I28 and controlled to vary the speed of the motor by the manually rotatable shaft 83. Shaft I21 of the motor has secured thereto a pair of spaced iron or iron alloy discs I38 and I31 that are permanently magnetized and are similarly oriented on shaft I21 from the standpoint of their magnetic poles. Between the magnetized discs I38 and I31 there is disposed a disc I38 of copper, aluminum or other non-magnetic metal. Preferably the axial aperture in disc I38 is sufficiently greater in diameter than shaft I21 that the disc does not engage the shaft and the disc may be supported by radially extending tension springs I38. It is also preferable that the thickness of disc I38 be less than the space between the magnetized discs I38 and I31 so that the disc I38 may be supported out of engagement with either of the discs 138 and I81 and no tendency. to rotate shall be imparted to disc I38 by the discs I38 and I31 through frictional engagement.

Disc I38 has secured thereto an arm I preferably of insulating material, which has secured thereto an electrical contact block I42. On one side of contact I42 in a plane at right angles to the axis of shaft I21 is a contact I43 and on the other side is a contact I44 similar to the contact I43. Contacts I43 and I44 are so spaced that when disc I38 is freely supported by springs I33 without torque being applied thereto, contact I42 is about midway between contacts I43 and I44.

Disc I38 has opposed tension springs I48 and I41 connected to its arm I. The remote end of spring I48 is connected to a fixed mounting I48 and the remote end of spring I41 relative to the arm I of disc I38 consists of or is connected to a flexible strand or cable which is wrapped several times around a sleeve I43 and has its free ment therewith so that when shaft 33 is rotated by means of crank 98 the tension upon springs I41 and I48 will be increased or decreased. Sleeve I43 has secured thereto a flange or disc I5I which is engageable by a flexible locking brake lever I52 which may be urged into engagement with disc I5I by means of the button-headed rod I53. Disc I5I is also provided with a laterally extending stop pin I54 which is engageable with a stop post I58 for limiting the rotation of sleeve I43 to substantially one revolution.

The magnetic drag unit comprising discs I38, I31 and I38 comprises a motor reversing and speed regulating mechanism. For this purpose motor I28 may be of the capacitor type, for operation on alternating current, having two field windings and a capacitor connected in delta arrangement. One side of the source of alternating current is connected to contact I42 supported by disc I38 and the other side of the source is connected to the apex of the two field windings otmotor I20. .The two fixed contacts I 43 and I rotated in the direction to impart counter-clock-.

wise rotation to shaft 93 as viewed from the lefthand end. This unwinds the cable which is connected to spring I67 and reduces the tension of that spring thereby permitting spring M6 to pull contact II? into engagement with stationary ated manually with motor I28 not running, or II v the speed of the motor has been adjusted to drive contact I. This causes the field of motor I28 rotate in clockwise direction they impart a torque to disc I38 tending to rotate it in clockwise direction also and when this torque exceeds the force by which contact I42 is held in engagement with contact I, which is the difierence between the forces exerted by springs I46 and I41, contact M2 will be moved out of engagement with contact IN. This opens the circuit of motor I28 whereupon it begins to deceierate andthe torque on disc I38 is reduced thus permitting it to return to engagement with contact I 46. With a steady supply voltage for operating motor I28 a conditlon of substantial equilibrium will develop under which motor I28 will operate at a steady speed just below that which would cause contact I62 to move out of engagement with contact Mt. Thespeed of the motor I28 may be increased byfurther rotating sleeve, I69 in counter-clock wise direction to further decrease the tension of spring I41, whereby a greater torque will be required to disengage contact M2 fnom contact Md.

Conversely, the speed of motor I28 may be decreased by rotating sleeve I49 in clockwise direction by means of crank wheel 98 to increase the tension of spring It! so that'a lesser torque is 1 required to disengage contact M2 from contact If the motor I28 is to be driven in countera clockwise direction sleeve I 39 is rotated clockwise until contact It? has been brought into engagementwith contact Hi3. This, completes the circuit of the motor for driving shaft I21 in countcr-clockwise direction. The torque imparted to disc I38 then tends to move the disc in counter-clockwise direction. The'speed may r be increased by increasing the tension of spring M1 and may be decreased by decreasing the tension. It will be noted that this is the reverse of the methodof increasing or decreasing the speed of motor I28 when it is driving shaft I21 in clockwise direction. Each time that the speed of motor I28 or its direction of operation is to be changed crank wheel 98 is rotated manually in potential dividers 3G and 31 in unison with potential dividers 2i and 28 but there is a phase difler- I ence to be corrected, crank wheel 89 is rotated with pin I53 depressed to lock flange IBI. Under either of these conditions the motor governor will not be disturbed while contact arms and are rotated manually. In the case of phase correction, the manual rotation will be in additive or subtractive relation to that being imparted by the driving motor.

Shaft 19 may be connected to and control a computing device for performing mathematical calculations based upon the changing position of the contact arms 45 and 50 of the potential dividers 36 and 31 necessary. to keep the galvanometers at zero deflection. An understanding of the nature of such calculating device is not essential to an understanding of the present invention. However, it'may be desirable to make visual observations based upon the changing positions of the contact arms of the potential dividers at the receiving station, such as for the purpose of plotting the course of movement of the object upon which the optical device II at the transmitting station is trained. Furthermore, since the potential divider contact arms 45 and 50 may be continuously moving and the movement of the contact arm 35 of potential divider 36 may be relatively rapid, it may be desirable toarrest the visual indicating means while readings are being taken without, disturbing the continued movement of the potential divider contact arms.

. fixed scale I64. Disc I62 has pivoted thereto a lever arm I65 which carries at its free end 9. depending pin I61 extending through slot I86 in disc I62. Lever arm I66 is biased by a tension spring I68 to urge lever arm I66 toward sleeve Pin I51 carries at its lower end a roller Ida which engages the periphery of the heartshaped cam ISI. A normally disengaged friction brake lever III is operable into engagement with the periphery of disc I62 by means of push button I12 for arresting disc I62 and indicator pointer I83.

Upon the operation of brake III to arrest indicator pointer I83, with heart-shaped cam Iiii continuing to rotate with the contact arm of potential divider 36, roller I89), rolling against the periphery of cam IBI will be moved outwardly from the axis of cam IBI as portions of the cam of increasing radius are presented to the roller. spring I he yielding to permit the movement of the lever arm It's as. roller I59 is cammed outwardly. After the taking of a reading of the position of indicator pointer I83, friction brake II I is released by releasing the pressure upon push button W2, Disc I62 is thus released and spring I58 which yielded to permit movement of roller led along portions of the periphery of cam IdI of increasing radius, causes roller $9 to roll along the periphery of cam I5 I to the pointof minimum radius, and roller I69, acting through pin It'i carries disc m2 around, with it thus restoring indicator pointer I63 to a definite angular position in relation to cam IN and thus to the contact arm 45 of potential divider 36, which has a fixed relation to cam ISL It will be apparent that roller-469 will return to the notch of cam ISI either clockwise or counter-clockwise depending upon which is the shortest route from the point engaged by the roller at the time that brake I'H is released. As shown in Fig. 4 the shaft llll has a similar heart-shaped cam and roller mechanism for driving degree indicator pointer I18.

The crank wheel 1 l9 and gear H1 afford means for adjusting the full degree potential divider 31 to add or subtract whole degrees under the circumstance that the potential divider 31 is considerably out of step with the potential divider 2| at the transmitting station. When crank wheel H9 is rotated it imparts rotation to shaft I08 through gears H1 and H4, sleeve H3, gear H6 and planetary gears i ll and H2. The gear ratios are such that rotation of crank wheel I 19 through a half revolution moves the contact arm 52 of potential divider 31 through a distance cor responding to one degree. which is the distance from one contact to the next on the potential divider 3?. This is the reason for the provision of the diametrically opposed recesses with which detent l32 cooperates. A correction of this sort may be effected while the shaft ill is being driven from shaft 32? and corrections amounting to whole degrees will be added to shaft Nil if in concluding a correcting operation shaft i la is brought to rest with detent lfif. engaging one of the recesses Hill, which is the correct procedure.

A modified transmission system is shown in Hg. 6. This system contemplates the provision of only one potential divider for representing instrument readings at the transmitting station and one potential divider for reproducing instrument readings at the receiving station. These potential dividers are arranged to represent hundredths degree values and correspond to the potential divider 2% in 2 and 36 in Fig. 3. As previously stated supplemental telephonic or telegraphic communication may be employed between the transmitting and receiving station and under certain circumstances such supplemental communication may be almost steady, so that it would be feasible to transmit whole degree information over the supplemental communication channel, leaving only the hundredths degree information to be transmitted under direct control or" the optical instrument and. registered by a single p= tential divider at the receiving station.

in Fig. 6 the reference numeral the hundredths degree potential divider at the transmitting station and the reference numeral 202 designates. the hundredths degree potential divider at the receiving station. Power supply lines 203 and 204 are connected to the end contacts of the potential divider 20! and extend to the receiving station where each is connected to one terminal of potentiometers 205 and 2M, respectively. The potentiometers 208 and 20'! correspond with the potentiometers 3i and 32 in Fig. 3 and serve to balance the resistance of the power supply conductors 223 and 204. The other ends of the potentiometers 205 and 201 are connected through resistors 289 and 2l0 to the two end terminals 01 receiving potential divider 2ll2 The contact arms of balancing potentiometers 206 and 201 are connected to the terminals of a power supply battery 208 by means of which potential differences are impressed across the potential dividers 201 and 202, such potential differences being equalized by the potentiometers 206 and 201.

Potential divider 201 is provided with separate main and auxiliary contact arms or brushes 2H and 2l2, respectively, which engage diametrically opposite contacts of the potential divider, are insulated from each other, and are connected directly or by means of individual collector rings 2l3 and 2, respectively, to galvanometer conductors H6 and 2H, respectively. The galvanometer conductors 216 and 2H include galvanometers H8 and H9, respectively, at the transmitting station and extend to the receiving station where they are connected to the back and front contacts, respectively, associated with the upper armature of a relay 22l. The upper armature of the relay 22| is connected to one terminal of a galvanometer 222.

The potential divider 202 at the receiving station has main and auxiliary contact arms or brushes 223 and 224, respectively, which are connected directly or through individual collector rings 226 and 221, respectively, to the back and front contacts associated with the lower armature of relay 22L The lower armature of relay 22l is connected to the middle contact of the lower bank of a three-point multiple bank switch 228 which is used for the same purpose as the multiple hank switch in Fig. 8, namely for arranging bridge circuits for balancing the power supply conductors 223 and 255. The lower switch arm or" switch 228 is connected to the other terminal of galvanometer 222. The upper and lower contacts or" the lower haul: of multiple canlr switch 228 are connected to the two end terminals of potential divider 282. One terminal of relay 225 is connected to one terminal of battery 229, the other terminal of which is connected to the switch arm associated with the upper bani:

of switch The middle contact of this bank is the only one having a connection and it is connected to one of two collector arcs associated with potential divider 222. The other of the two collector arcs 23H is connected to the other terminal of relay 22s and the two collector arcs are bridged by a brush 232 which is insulated from but moves with the diametrically opposed contact arms or brushes 223 and 2%.

The power supply conductors 2d? and 235s are individually balanced to produce equal potential differences across potential dividers 2M and N2 in the same manner as described in connection with Fig. 3, namely, by setting the main brush 325i on first one and then the other of the end contacts of potential divider and moving switch to one and then the other of the on treme positions. At the upper contact bani: the circuit of relay 22l is interrupted so that the armatures are released to their hack. contacts, thus opening the galvancmeter conductor 2i?! and connecting galvanometer conductor tit through galvanometer 222 to the switch arm associated with the lower bank of switch 228. By means of this switch arm the galvanometer 222 is connected first to one and then to the other of the end terminals of potential divider 202, the effect of which is to switch the full resistive circult of potential divider 292 from one to the other of two arms on opposite sides of the galvanometer conductor. These switching operations are coordinated, by means of telephonic or telegraphic communication, with the movement of the main brush 2H of potential divider 20! from one to the other of the two end contacts of that potential divider, the effect of which is to switch the entire resistive circuit of the potential divider from one to the other of the two remaining arms brush 2|! of that potential divider.

of the bridge circuit on opposite sides of the galvanometer conductor.

After the power supply conductors have been balanced switch 228 is restored to the middle 1 cuit of relay 22! is open and the galvanometer circuit is traced from the main brush 223 of potential divider 202 through the inner collector rings 226, the 'back contact and lower armature of relay 22!, the middle contact and switch arm of the lower bank of switch 228, the galvanometer 222, the upper armature and back contact of relay 22!, galvanometer conductor 2i6 including galvanometer 2!!! to the inner collector ring 283 of potential divider 20! and thence to the main However, when brush 232 moves into bridging relation to the conductive are 23! it completes the energizing circuit for relay 22! and the galvanometer circuit is then traced from the auxiliary brush 22d of potential divider 202 through the outer collector ring 221, the lower front contact and armature of relay 22!, the middle contact and switch arm of the lower bank of switch 228, galvanometer 222, the upper armature and front contact of relay 22!, galvanometer conductor 2!! including galvanometer M9 to the outer collector ring 2H8 of potential divider 2M and thence to the auxiliary brush 2l2. From this it will be apparent that neither of the brushes of potentiometer 202 has control of a galvanometer circuit when it is approaching or'passing over the end contacts of the potentiometer, and assuming that potentiometer 202 is closely tracking potentiometer 20 l ,which is a normal mode of operation, neither of the brushes of potentiometer 20! will have control of a galvanometer circuit when it is approaching or passing over the end contacts of that potentiometer. It follows from this that no relatively large potential of reverse polarity is ever suddenly impressed on a galvanometer conductor, for the avoidance of which the rectiher and relay circuits were provided in the system shown in Fig. 3. As distinguished from the system shown in Figs. 2 and 3 the system shown in Fig. 6 provides that the galvanometer deflection at the transmitting station shall always correspond in direction and magnitude with the galvanometer deflection at the receiving station, this being accomplished by switching from one to the other of the galvanometers H8 and 2l under the control of relay 22! at the receiving station. The system shown in Fig. 6 is therefore more readily adapted to transmission in the reverse direction under the circumstance that the receiving station'wishes to instruct the attendant at the transmitting station to scan a particular area or train the optical device on a distant object of which the operator at the receiving station has knowledge.

The electrical system of Fig. 6 comprising only one potential divider at each station for instrument reading transmission may employ the same mechanical operating mechanisms as the electrical system shown in Figs. 2 and 3. For example, m Fig. 1 thepotential divider 201 would potential divider 26 would be omitted together with its driving gear and shaft 22 and 23, respectively, and its shifting cam and follower mechanism including cam 21, bell crank 29 and link '32. At the receiving station, referring to Fig. 4, the potential divider 202 of Fig. 6 would be substituted for the potential divider 36. Potential divider 31 would be omitted together with cam and follower mechanism for shifting it in the manner shown in Fig. 1. However, shaft I! and the heart-shaped cam and roller mechanism for driving indicator pointer I16 may be retained, because although the attendant at the transmitting station will inform the operator at the receiving station from time to time by telephone or telegraph as to the whole degree reading of the optical device H, it is advisable to have both the degree and hundredths degree indicators at the receiving station so that the receiving station has a complete register of the reading of the optical device II which is continuously correct as long as the attendant at the transmitting station is following a particular moving object and makes no sudden and substantial change in the position of optical device II. with which the operator at the receivbe mentioned that optical instruments of the type shown in Fig. 1 are sometimes provided with means for disengaging the driving worm l6 from the driven worm wheel it whereby the optical device may be swung through a wide angle without any accompanying rotation of shaft IT. Under such circumstances, it would be necessary for the attendant at the transmitting station to inform the operator at the receiving station as to where the indicator pointer I76 should be set to register correctly the degree reading of optical device i l. The operator can then bring the hundredths degree indicator pointer I63 into the correct position by balancing the potential divider system so that the galvanometer 222 will show zero deflection.

It has been set forth previously that the potential divider 31 represents only a part of a revolution of optical device I! such as 30 degrees, for the reason that itmay not be feasible to provide potential dividers having 360 contact points to represent in one revolution of its contact arm a full revolution of optical device ii. However, when a system of the type shown in Fig. 4 employs no potentiometer for full degrees corresponding to potential divider 31 the scale with which indicator pointer I cooperates may he graduated to indicate 360 degrees and such gearing may be employed between shaft I9 and shaft in! as to cause shaft IDI to execute one revolution for 360 revolutions of shaft I6; Thus the pointers I63 and I16 will give direct readings of the positions of optical device Ii.

Although certain specific embodiments of the invention have been shown in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to such specific embodiments but is capable of modification and rearrangement without departing from thespirit of the invention and within the scope of the appended claims.

What is claimed is:

1. In a measuring system, a potential divider, means for adjusting said potential divider according to the characteristic to be measured, a second potential divider, means for adjusting said second potential divider, a common source of potential for said potential dividers, a galvanometer conductor extending between said potential dividers, a galvanometer associated with said conductor for indicating disparity between the adjustments of said potential dividers, and automatically operable means for limiting the current through said galvanometer when said conductor receives opposite extremes of potential from said potential dividers.

2. In a measuring system, a potential divider, means for adjusting said potential divider according to the characteristic to be measured, a second tential divider, means for adjusting said second potential divider, a common source of potential for said potential dividers, a galvanometer conductor extending between said potential dividers, a galvanometer associated with said conductor for indicating disparity between the adjustmentsof said potential dividers, and'automatically operable means for reversing the flow of current through said galvanometer and for limiting said current when said conductor receives opposite extremes of potential from said potential dividers.

3. In a measuring system, a potential divider, means for adjusting said potential divider according to the characteristic to be measured, a second potential divider, means for adjusting said second potential divider, a common source of potential for said potential dividers, a galvanometer conductor extending between said potential dividers and having a plurality of resistors in series therein, a galvanometer, a relay for connecting said galvanometer in shunt with either of two of said resistors in opposite polarity relationship, and a rectifier in shunt with another of said resistors for supplying energizing current for said relay irrespective of the direction or flow of current through said conductor when said conductor receives opposite extremes of potential from said potential dividers.

4. In a measuring system, a potential divider, means for adjusting said potential divider according to the characteristic to be measured, a

second potential divider, means for adjusting said second potential divider, a common source of potential for said potential dividers, a galvanometer conductor extending between said potential dividers, a galvanometer for indicating disparity between the adjustments of said potential dividers, means for reversing the connective association of said galvanometer with said conductor, and means associated with said conductor for operating said reversing means irrespective of the direction of current through said conductor when said conductor receives opposite extremes oi potential from said potential dividers.

5. In a signaling system, a station having a potential divider, means for adjusting said potential divider in accordance with information to be transmitted, said potential divider having a pair of diametrically opposed electrically independent contactors rotatable in unison, a second station having a potential divider, said potential divider having a pair of opposed electrically independent contactors rotatable in unison, means for adjusting the potential divider at said second station. a pair or conductors extending between said stations and interconnecting said potential dividers, means at one of said stations for supplying a source of potential between said conductors, a pair or salvanometer conductors extendin: between said stations, a salvanometer at said one station connectable to one galvenometer conductor and to one of the contmtors of the potential divider st slid station or to the other geldividers, and a pair of galvanometers at said other station each having one terminal connected to one of said galvanometer conductors and each having the other terminal connected to one of the potential divider contactors at said other station.

6. In a signaling system, a station having a potential divider, means for adjusting aid potential divider according to information to be transmitted, a second station having a potential divider, means for adjusting the potential divider at said second station, a galvanometer conductor extending between said potential dividers, a galvanometer associated with said conductor for indicating disparity between the adjustments of said potential dividers and automatically operable means for protecting said galvanometer from opposite extremes of potential at said potential dividers.

7. In a signaling system, a station having a potential divider, means for adjusting said potential divider in accordance with iniormation to be transmitted, a second station having a potential divider, means for adjusting the potential divider at said second station, a galvanometer conductor extending between said potential dividers, a galvanometer associated with said conductor for indicating disparity between the adjustments of said potential dividers and automatically operable means for limiting the potential difference applicable to said galvanometer to a safe value substantially less than the'opposite extremes of potential at said potential dividers.

8. In a signaling system, a station having a potential divider, means for adjusting said potential divider in accordance with information to be transmitted, a second station having a l otential divider, means for adjusting the potential divider at said second station, a galvanometer conductor extending between said potential dividers, a galvanometer associated with said conductor for indicating disparity between the adjustments or said potential dividers and automatically operable means for precluding the application to said galvanometer of the opposite extreme of potential at said potential dividers.

WALTER. KOENIG, JR.

REFERENCES crrEn The following references are of record in the tile or this patent:

UNITED STATES PATENTS 

